Adhesives and in particular adhesives comprising olefinic polymers are well known in the art and enjoy widespread usage throughout the industry. Typical areas of application of such adhesive include hygienic articles and in particular disposable absorbent articles, packaging materials, automotive parts, and the like.
Adhesives made from commonly used polyolefins such as PP, PE, PS, PIB have a number of useful properties. They are bio-compatible and food compatible, chemically stabile, inert, non toxic materials. However, most of them have poor mechanical properties including insufficient strength/tear resistance, insufficient stretchability/elasticity and the like.
Other adhesives, such as PU based adhesives, have also been widely used for example because of their elastic properties. PU adhesives however have the disadvantage that they are polymerized from the very toxic monomer isocyanate and hence can not be used for many application due to their inherent toxicity caused by residual monomer content.
Several approaches have been proposed in the prior art to provide elastic properties to such adhesives. The most commonly used approach is based on changing the chemical structure of the polymer by introducing hinged joints/moieties into the main chain of the polymer. These side groups or side chains provide more flexibility to the polymeric backbone preventing crystallization of polymer, lowering the glass transition temperature (Tg) and improving the elasticity of the resulting material. Usually, the hinge groups contain heteroatoms providing flexibility such as oxygen, nitrogen or chlorine placed into the main chain or into bulky side groups. Another approach is mastication of the polymer by blending with special plasticizing agents. Both approaches, however, require heteroatoms to be introduced into the molecule or into the bulk of the coating material.
The third approach proposed in the prior art to provide elastic properties to such adhesives, which is more close to the present invention, is to exploit the formation of hetero-phases which reinforce the bulk material by forming a physical net. To do this the block-co-polymerization of two or more different monomers has been used leading to polymeric backbones comprising blocks with different Tg. This results in micro-phase separation in the bulk with formation of reinforcing crystalline domains of one co-polymer linked with each other by flexible chains of the second co-polymer.
In essence, conventional adhesives carry a wide variety of inherent disadvantages including but not being limited to insufficient strength/tear resistance, insufficient stretchability/elasticity, not being bio-compatible, not being food compatible, comprising heteroatoms such as chlorine and hence leading to toxic residues when burnt, and the like.
It is an object of the present invention to provide adhesives which overcome the disadvantages of the prior art adhesives.
It is an further object of the present invention to provide articles which comprise elastic adhesives.
It is an further object of the present invention to provide a method for manufacturing adhesive of the present invention.